Load handling device with servo feed-back control

ABSTRACT

The invention concerns a handling device comprising, in combination, a mechanical equilibrium mechanism ( 10 ) with low reaction time, having an arm ( 20 ) whereof the proximal end ( 22 ) is locked on a pivot pin ( 18 ) and whereof the distal ( 26 ) is adapted to support a load ( 10 ), a force sensor ( 30 ) positioned in a selected site for detecting apparent weight variation the load ( 10 ) resulting from a force being exerted on said load in response to an operator&#39;s movement, servo feed-back means ( 32 ) actuated by the force sensor ( 30 ), and an actuator ( 34 ) controlled by the servo feed-back means ( 32 ) and connected to the arm to assist the operator&#39;s movement. The invention is applicable in particular to robot arms or the like.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a National Phase Patent Application of InternationalApplication Number PCT/FR01/00642, filed on Mar. 5, 2001, which claimspriority of French Patent Application Number 00/03047, filed Mar. 9,2000.

The invention relates to a load handling device.

Load handling devices are already known which generally comprise an armpivotably mounted about a usually horizontal axis, in order to effectdisplacement of the load in a substantially vertical direction.

Such devices are used in particular for controlling a robot arm used forhandling a load which may be a tool, for example.

Such devices must make it possible to give assistance to the operator,so that he can displace the load without special effort.

In other words, the handling device must be provided with a boosterfunction to permit such handling without effort on the part of theoperator.

Until now, such a booster function has been effected by three types ofsolution.

First of all, pneumatic solutions are known comprising a jack, whichprovides suspension of the load and/or vertical displacement thereof.Such solutions, whilst giving relatively satisfactory results for smallloads, become impossible to manage as soon as the air volume of the jackgoes above about 1 dm³. This is due to the losses of load, whichgenerate variations in pressure between the different points of thecircuit, as well as to the compressibility of the air. Such pneumaticmeans have the disadvantage of having a response time in seconds, i.e.too great a time not to be felt by the operator.

Mixed solutions are also known, wherein a pneumatic system is coupled toa counterweight. These solutions, which give the same results as theabove-mentioned solutions, have the further disadvantage of greatlyincreasing inertia, which can adversely affect the horizontal movementsof the load even more.

Electrical solutions are also known, which generally imply the use oftypes of automatic load-controlling lifting blocks. These solutions havethe disadvantages on the one hand of being sophisticated (risk ofbreakdown) and on the other hand of needing a weighing phase duringwhich the load is not controlled and may pose a danger to the operator.

Thus in these three types of solution, the booster function for handlingis barely ensured.

The object of the invention is in particular to overcome theabove-mentioned disadvantages.

It aims in particular to procure a load handling device which isequipped with means which are simple to realise and which allowassistance to be given to handling.

It also aims to procure a handling device such as has the furtheradvantage of having a rapid response time, so as not to be felt by theoperator.

The invention proposes to this end a load handling device whichcomprises, in combination:

a mechanical equaliser with a rapid response time, comprisingcounterbalancing means housed in this body and acting on rotary shaft,as well as an arm whose proximal end is fixed to the rotary shaft andwhose distal end is capable of carrying the load, and

a booster mechanism comprising an effort sensor located at a selectedsite in order to detect a variation in apparent weight of the loadconsequent upon a force exerted on that load following a movement of anoperator, servo means actuated by the effort sensor, and an actuatorpiloted by the servo means and connected to the arm in order to boostthe movement of the operator.

Thus the invention resides in the combination on the one hand of amechanical equaliser with a rapid response time, comprising essentiallyan arm connected to counterbalancing means and, on the other hand, aservo mechanism coupled to this arm in order to assist handling of aload carried by the arm.

By way of non-limiting example, an equalizer, also calledcounterbalancing device, of the type described in U.S. Pat. Nos.4,620,829 and 4,901,591, the entire contents of which are incorporatedherein by reference, can be used.

Such devices, which are purely mechanical, are used in particular forcounterbalancing the forces acting on an arm stressed by a load, such asa tool. They therefore make it possible to obtain strictcounterbalancing of the arm, whatever its angular position relative tothe body on which it is articulated. Normally, the arm can pivot through360° relative to the body, which allows the load to describe a circulartrajectory.

In a counterbalancing device of this type, the operator can displace theload, e.g. a tool, virtually without effort, since the counterbalancingdevice compensates for the forces acting on the arm, whatever theangular position of the arm about its rotatable axis of articulation,which is generally horizontal.

In the invention, the rotary shaft of the arm of the equaliser ispreferably substantially horizontal.

The effort sensor is provided to detect a variation of apparent weightof the load. It must be capable of detecting a difference in effort,however slight, generated by the operator on the load, in which casethis difference may range from a few hundredths of a gramme to severalkilogrammes.

The effort sensor is advantageously incorporated in a deformablemechanical structure capable of feeding back to the sensor the verticalcomponent of the efforts resulting from the weight of the load.Preferably, this deformable mechanical structure is interposed betweenthe distal end of the arm and the load, and comprises a parallelogram.

In the invention, the booster mechanism is provided to effect a verticaldrive, in either direction, from the detection supplied by the effortsensor. This makes it possible to ensure, relative to the prior devices,considerable reduction in hysteresis as well as the effects of inertiafor which the efforts of the operator have to compensate.

It should be emphasised that such results cannot be obtained except inthe extend to which the booster mechanism supplies motor power which isapplied to a small part of the load, whereas the majority of the effortlinked to the weight are compensated by the equaliser proper, both withregard to the residual effort and the response time, withoutcontributing inertia or substantial friction.

A mechanical equaliser, such as described in the above-mentioned patentsmakes it possible to obtain such high-precision counterbalancing.

The actuator of the assistance mechanism is advantageously connected toa support and to a rocker bar connected to the arm.

In a preferred embodiment of the invention, the actuator is a pneumaticjack, in particular with a volume of less than 1 dm³. This small volumemakes it possible to confer on the pneumatic jack operating parameters,particularly with respect to response time, which make it compatiblewith the features necessary for the handling comfort of the operator.

The pneumatic jack is advantageously controlled by servo means through aproportional valve.

Obviously, the servo means make it possible to pilot the actuator, e.g.a pneumatic jack, which boosts the desired movement by the operator.This boosting is therefore effected by simple pressure exerted by theoperator directly on the load and not by action on a control knob.

In the following description, given purely by way of example, theattached drawings will be referred to, which show:

FIG. 1, a diagram of a handling device, according to a first embodimentof the invention; and

FIG. 2, a diagram of a handling device, according to a second embodimentof the invention.

FIG. 1 will be referred to first, which shows a handling deviceaccording to the invention. This device comprises a mechanical equaliser10, with a rapid response time, comprising a body 12 fixed to a support14 (itself fixed or mobile). The body houses on its interiorcounterbalancing means 16, which for example may be identical or similarto those described in the U.S. Pat. No. 4,620,829 or U.S. Pat. No.4,901,591 cited above, which may be referred to for fuller information.

The counterbalancing means 16 act on a pivot pin 18 carried by the body12 and extending, in the example, in a substantially horizontaldirection. The equaliser 10 comprises an arm 20 having a proximal end 22locking on the shaft 18 and a distal end 24, also referred to as thefree end.

The arm 20 may rotate about the pivot 18 so that its free end 24describes a circular trajectory, in which case the degree of movement ofthe arm may be between 0 and 360°.

The end 24 of the arm 20 forms an articulated link for a link element 26at the end of which a load 28 may be attached. Due to the articulatedlink, the centre of gravity of the entire suspended mass (link element26 and load 28) is positioned without effort and, obviously,perpendicular to the end 24 of the arm.

In the example, the horizontal shaft 18 forms the output shaft of themechanical equaliser 10 and produces a sinusoidal torque.

As already indicated, such a mechanical equalizer is known per se andmay be realized, for example, according to either of the above-mentionedpatents.

In a counterbalancing device of this type, the counterbalancing means 16are adjusted to provide counterbalancing depending on a specified loadand thus to allow an operator to control this load without particulareffort and in a short response time.

However, often the load carried by the arm varies in time.

An example can be found in an application where the load is a grippingdevice having its own weight and to which may be attached, during anoperating cycle, one or more loads whose actual weight has just beenadded to that of the gripping device itself.

The result is a difference in load which means that the value of theload is no longer the same as that for which the equaliser has been setat the start.

Furthermore, such a counterbalancing device generally produces friction,however slight, which the operator has to overcome in handling the load.

With the invention, it is possible to take into account variations inload and friction inducted by the equaliser.

To this end, a servo mechanism is further provided which comprises firstof all an effort sensor 30, e.g. of the electric type, located in aselected place to detect a variation in apparent weight of the load 28.This effort sensor must be appropriately incorporated in the linkelement 26, i.e. between the free end 24 of the arm and the load 28itself.

This effort sensor continuously measures the weight of the load 28 andtransmits this information to servo means 32 which are thus actuated bythe effort sensor. These servo means 32 pilot an actuator 34, which islinked to the arm 20 in order to boost the movement of the operator. Inthe example, the actuator 34 is a pneumatic jack whose end is fixed tothe support 14 and whose other end is connected to a rocker bar 36connected to the arm 20. The pneumatic jack thus acts synchronously withthe equaliser.

The sensor 30 makes it possible to detect differences in apparent weightof the load relative to a reference value (this small differences aredue to the action of an operator trying to move the load 28 down or up)and adjust the pressure in the jack 34 so as to assist the operator inthe movement that he wishes to make.

The handling device of FIG. 1 shows a simple assembly. However, it ispossible to provide more sophisticated assemblies, as is shown in FIG.2.

In this figure, as in FIG. 1, an equaliser 10 can be found having an arm20, which is articulated about or fixed to a shaft 18 and a boostermechanism identical or similar to that described above and comprising aneffort sensor 30, servo means 32 and an actuator 34 interposed betweenthe support 14 and a rocker bar 36 connected to arm 20.

However, the arm 20 and the effort sensor 30 form part of a moresophisticated assembly.

The load 28 is supported vertically by a link element 38 carried at theend 40 of a horizontal arm 42, whose other end 44 is mounted at thelower end of a vertical shaft 46 capable of pivoting on itself, in sucha manner that the arm 42 can describe a rotary movement relative to theshaft 46. This shaft 46 is fixed to a four-bar mechanism 68 whichcomprises two parallel rocker bars 48 and 50, substantially horizontaland articulated respectively by points 52 and 54 on the shaft 46 and bypoints 56 and 58 on a vertical shaft 60. This shaft 60 is articulated tothe end 24 of the arm 20 of the equaliser and is articulated at 62 tothe end of an arm 64 mounted parallel to the arm 20 and articulated by apoint 66 to the support. Thus the shaft 60, in combination with the armand the arm 64, forms a deformable parallelogram mechanism, in which theshaft 60 remains vertical.

The vertical shafts 46 and 60, as well as the rocker bars 48 and 50(also known as horizontal shafts) form a deformable mechanical structureof the said parallelogram 68. The rocker bar 48 is held in a horizontalposition via the effort sensor 30, which is fixed to the end 70 of a bar72, in turn fixed rigidly at 74 to the vertical shaft 60.

The effort sensor 30 is deformed very easily according to the effort towhich it is subjected and which it measures. The horizontal position ofthe rocker bar 48 is not strictly perfect, but sufficient not to distortthe operation of the mechanism, taking into account the size of themeasurement values necessary for it to function well.

It is essential that the deformable parallelogram 68 ensures that theshaft 46 is in a vertical position whilst feeding back to the sensoronly the vertical component of the efforts generated by the weight ofthe load, whatever the position of the load relative to the verticalshaft 46, both in rotation about this shaft 46 and in radial translationrelative to this shaft 46.

Furthermore, the shaft 60 ensures free rotation of the assembly aboutthe points 56, 58, 24 and 62.

The shaft 60, as well as the arms 20 and 64, form a deformableparallelogram 76, which keeps this shaft 60 vertical.

Thus, as in the previous embodiment, the equaliser 10 effectscompensation for the majority of the weight of the load as well as ofthe mechanical structure forming the two parallelograms 68 and 76.

The sensor 30 continuously measures the weight of the load and transmitsthe value to servo means 32, which themselves pilot the actuator 34, inthe same manner as in the preceding embodiment.

Obviously, the invention is not limited to the embodiments describedabove by way of examples but extends to other modifications.

Obviously the equaliser itself is capable of being subjected to numerousmodifications, and is not limited to a mechanical equaliser of the typeof those described in the above-mentioned French patents.

Thus for example, the rotary shaft or output shaft of the equaliser isused as a base, either of a rotating arm, or of a parallelogram.However, other assemblies are conceivable, in particular an assemblywhere the equaliser is not incorporated into the structure of the deviceand where a transmission effects synchronisation of the movements andtherefore of efforts.

In the same way, the booster mechanism is capable of being modified inmany ways, and it is possible to provide other servo means than thosedescribed above.

Although the actuator is preferably a pneumatic jack, it is conceivableto use other types of actuator capable of forming a drive for the arm.

1. A device for handling a load, comprising: a mechanical equaliserincluding counterbalancing means acting on a rotary shaft and havingreturn means capable of adjusting the counterbalancing depending on theload, as well as an arm whose proximal end is fixed to the rotary shaftand whose distal end is capable of supporting the load; an effort sensorlocated at a selected site in order to detect a variation in apparentweight of the load resulting from a force exerted on the load directlyby a human operator; servo means actuated by the effort sensor; and anactuator piloted by the servo means and connected to the arm in order toassist a movement of the load by the human operator.
 2. The deviceaccording to claim 1, wherein the rotary shaft of the arm of theequaliser is substantially horizontal.
 3. The device according to claim1, wherein the effort sensor is incorporated in a deformable mechanicalstructure capable of feeding back to the effort sensor the verticalcomponent of forces resulting from the weight of the load.
 4. The deviceaccording to claim 3, wherein the deformable mechanical structure isinterposed between the distal end of the arm and the load and comprisesa parallelogram.
 5. The device according to claim 1, wherein theactuator is connected to a support and a rocker bar connected to thearm.
 6. The device according to claim 1, wherein the actuator is apneumatic jack having a volume of less than 1 dm³.